Hi, as the others have intimated, you have a mix of plecs there in the 55 with a real mix of requirements. I would suggest too many too, some of which really would not get on, ok this gets worse the larger they get but even small ones will start to divide territory.
The L134 can be really territorial. The L190, 191 and 027 will squabble as they are all the same. The food you are feeding is in my opinion not suitable for many of the plecs you have in there.
L104, L397, L190, L191, L027 all want a wood diet with veg like sprouts so that means plenty of wood they can feed on. Better with wood they can bite through like bog wood and not the harder mopani wood types.
The L201, L129, L134 all want a meaty diet, so shrimp, fish, mussels etc. Which the bristlenose will also rellish.
In the 75 you have a number of similar looking plecs which could mean disputes. Some fairly territorial plecs along with some real softies (L075, L200).
Note that you are also keeping high temp slow water plecs with lower temperature faster water plecs.
In general I think you need to look at a set up 55 or 75 for each kind/ habitat and thin them out somewhat. Plecs all have similar shapes but many different requirements and they don't do well overstocked without the habitat they prefer, which is not necessarily caves.
Get that sorted and I would expect better results.